Redeye is a phenomenon in flash photography where a flash is reflected within a subject's eye and appears in a photograph as a light, usually red, dot where the black pupil of the subject's eye would normally appear. The unnatural glowing red of an eye is due to internal reflections from the vascular membrane behind the retina, which is rich in blood vessels. This objectionable phenomenon is well understood to be caused in part by a small angle between the flash of the camera and the lens of the camera. This angle has decreased with the miniaturization of cameras with integral flash capabilities. Additional contributors include the relative closeness of the subject to the camera and ambient light levels.
The redeye phenomenon can be reduced by causing the iris to reduce the opening of the pupil. This is typically done with a “pre-flash”, a flash or illumination of light shortly before a flash photograph is taken. This causes the iris to close. Unfortunately, the pre-flash is an objectionable 0.2 to 0.6 seconds prior to the flash photograph. This delay is readily discernible and easily within the reaction time of a human subject. Consequently the subject may believe the pre-flash is the actual photograph and be in a less than desirable position at the time of the actual photograph. Alternately, the subject must be informed of the pre-flash, typically losing any spontaneity of the subject captured in the photograph.
Digital photography eliminates the need for film as the image is digitally captured and stored in a memory array for display on a display screen on the camera itself. This allows photographs to be viewed and enjoyed virtually instantaneously as opposed to waiting for film processing. Digital photography equipment includes microprocessors for image processing and compression and camera systems control. It is possible to exploit the computation capabilities of such microprocessors for performing operations to improve redeye detection and elimination.
Existing techniques for redeye detection and correction in digital images are described in U.S. Pat. No. 6,407,777 and US Patent Application Publication No. 2005/0232490. However, these prior methods are not efficient in practice.